Because carbon steel has the advantage of cheap price, good processing performance, convenient source of raw materials and so on, therefore for the manufacture of small plastic mold with simple shape or low precision requirements, the service life does not need a long plastic mold, the use of this kind of steel manufacturing.Chinese brands are often used in 45, 50, etc.At present, the steel Numbers widely used in the world are shown in table 1.
For the simple shape, small thermosetting plastic mold, due to the high wear resistance requirements with T7, T8, T9, T10, T11, T12 and other carbon tool steel manufacturing.
Second, carburized plastic mold steel
Type carburizing plastic die steel carbon content from 0.1% to 0.25% range, generally after annealing hardness is low, good machinability, the cutting mould processing and shaping the quenching after carburizing, not only has high strength after low temperature tempering, and the core has good toughness, mold surface of high hardness, high wear resistance, and also can guarantee good polishing performance.Another advantage is good plasticity, can use cold extrusion molding method manufacturing mold, without cutting processing, for mass production of the same shape of mold advantage.The disadvantage is that the mold heat treatment process is more complex, deformation.
Pre-hardened plastic mold steel
Prehardened plastic mold steel refers to the hot processing module, pre-conditioning treatment, in order to obtain the required performance, and then die processing, until the mold molding, no final heat treatment can be used directly.Thus, the mold deformation and crack caused by heat treatment can be avoided.Prehardened steel is most suitable for making large and medium precision plastic molds with complex shapes. The hardness of prehardened steel is generally in the range of 30-42hrc, especially in the high hardness zone (36-42hrc), with poor cutting performance.
Aging hardening plastic mold steel
For complex, high precision, the life of the plastic mould to keep the high life, mold material using a state must have a high comprehensive mechanical properties, therefore, must use the final heat treatment, however, with the final heat treatment (quenching and tempering) often leads to mold heat treatment deformation, namely the precision of the mould is difficult to meet the requirements.
Age hardening plastic die steel after solid solution hardening softening (28-34 HRC) can be cutting, aging treatment after cold forming, can obtain high comprehensive mechanical properties, aging heat treatment deformation is small, and this kind of steel in general has good welding performance, and can undertake surface nitriding advantages, suitable for manufacturing complex, precision plastic mold, high life.
Aging hardening plastic mold steel mainly includes two types, namely martensite aging steel and precipitation hardening steel.Martensite aging steel has a high strength/density ratio, good machinability and weldability and simple heat treatment technology, but its price is higher precipitation hardening steel precipitation hardening steel is one of the relatively new steel, it contains less alloying elements than martensite aging steel, especially the Ni content is much less.The hardness of the material is also about 30HRC in the state of solid solution treatment, which can be cut, and then aging treatment after the mold is made, so that the hardness is about 40HRC.And the aging deformation is very small (about 0.01%), suitable for manufacturing high hardness, high strength and high toughness precision plastic mold, see details:

Note: also commonly used: DAIDO NAK80, HITACHI HPM50
Integral hardened plastic die steel
Used to suppress thermosetting plastics, intercourse reinforced plastics (such as nylon reinforcement or glass fiber reinforced plastics) products mold, as well as the production batch is large, mould service life long plastic mold, generally selects high hardenability of cold work die steel and steel materials, these materials through the final heat treatment, can guarantee to use state high hardness, high wear resistance and long service life.
Corrosion resistant plastic mold steel
Corrosion resistant steel is mainly used in the production of chemical corrosion plastics (such as polyvinyl chloride or polystyrene with anti-burning agent, etc.) as raw materials of plastic products.Corrosion resistant plastic mould steel is divided into high carbon and high chromium corrosion resistant steel, high carbon and high chromium corrosion resistant steel, low carbon chromium and nickel corrosion resistant steel.
Medium carbon and high chromium corrosion resistant steels: 4Cr13, 420, 168, S136, M300, M310, HPM38, PAK90, etc
Low carbon cr-ni corrosion resistant steel: 1Cr17Ni2
Factors influencing the processing performance of steel mirror of plastic die
The production of transparent plastic products, especially optical instruments (such as lenses, etc.), for forming mold mirror processing performance requirements are very high.But strictly speaking, there is no special brand of mirror processing with plastic mold steel.
Generally, there are several factors influencing the mirror processing performance of the mold as follows:
(1) non-metallic inclusions, bubbles, oxides and sulfides in metallurgical quality steel are the main reasons affecting the formation of needle holes and holes in the mirror polishing and grinding of die steel;Therefore, the surface roughness of all plastic mold requirements are very high, generally can not use sulfur free cutting steel;Even if it is not free cutting steel, if the content of oxide and sulfide inclusions in steel is high, it is easy to fall off and form pinholes in the grinding process.Therefore, the use of vacuum smelting or electroslag remelting technology, will effectively improve the purity of steel, and thus improve the polishing performance of steel.
(2) uneven microstructure in steel is another reason that affects the polishing performance.Microscopic uneven regional organizations, and zonal segregation may make steel such as there was a very fine hairline in mirror machining and grinding, pit defect, in order to prevent segregation, must grasp the steel after the crystallization of ingot casting technology and quality, in addition to forging fully, to ensure the density of steel, if able to homogenization or esr smelting, heat treatment can effectively reduce the segregation, so as to improve the polishing performance of steel.
(3) the hardness of steel is high, which has a good effect on the mirror polishing performance.
(4) polishing technology in order to get a relatively low surface roughness, polishing technology also plays a big role.For example, the surface should be protected from temperature effects that may cause tissue changes during pre-grinding.Therefore, in addition to sufficient cooling, it is very important to choose the right grinding wheel.The grinding pressure plays a big role here, and when the grinding wheel is smeared, the pressure will accidentally increase, which will cause the temperature to rise.A better approach is to change the direction of the grinding frequently while grinding the surface.Polishing with diamond paste is the best way to get the best polishing results.When polishing, avoid excessive surface contact Angle pressure, otherwise the softer matrix will be eroded, resulting in carbide free, then cracking, and leaving defects.Hands and work pieces must be cleaned when switching to finer granularity.Of course, a special polishing tool should be used for each particle size.The polishing surface is mostly judged by the naked eye.However, due to the corresponding tone of nickel materials, the surface is often better than the actual situation, easy to lead to wrong judgment.